The overall objective of this proposal will be to investigate, virologically and immunologically, the natural occurring canine distemper of chronic and "old dog encephalitis" (ODE) forms of encephalitis. Studies will include additionally to learn whether canine distemper virus (CDV) antigen is present in brains of dogs after recovery or after prolonged period following an attack of the acute central nervous system (CNS) disease. The investigation will include virologic methods to determine the state of the CDV antigen in the brain. Attempts to isolate competent virus and to detect defective CDV will be made. Specialized isolation techniques will be used for brains of dogs with ODE and chronic encephalitis. Cell-mediated and humoral immune responsiveness of dogs with various forms of encephalitis and dogs that have recovered from acute CNS distemper infections will be examined. The neurological manifestations of canine distemper encephalitis have been shown to be similar to acute measles encephalitis, SSPE and possibly MS in man. These studies on the canine distemper model are aimed to provide better understanding on the pathogenesis of virus-induced demyelinating encephalitis.